Optical barrier device

ABSTRACT

The present invention relates to an optical barrier apparatus which scans a detection area with an optical beam, and when the scanning beam is blocked by an object so that a reflection beam is not received, notifies of object presence. An optical beam from an optical beam generating circuit ( 11 ) is reflected by a scan mirror ( 12 ) and a detection area ( 1 ) is scanned by a scanning beam (BM 1 ). The scanning beam (BM 1 ) is reflected by a reflector array ( 23 ) of another unit and received by a light receiving element ( 14 ), and the presence/absence of a pulse deficiency of light reception output is detected by a signal deficiency detection circuit ( 15 ). When the scanning beam (BM 1 ) is blocked by an object ( 30 ) so that a part of the reflection beam from the reflector array ( 23 ) cannot be received and a pulse deficiency occurs in the light reception output, an output (Z 1 ) from the signal deficiency detection circuit ( 15 ) becomes a logic value zero to thus notify of object presence.

TECHNICAL FIELD

[0001] The present invention relates to an optical barrier apparatusused in safety equipment and the like for industrial machinery. Inparticular the invention relates to an optical barrier apparatus (alsoreferred to as an optical barrier sensor) for scanning a detection areawith an optical beam, and judging the absence of object when areflection beam of the optical beam is received, and judging thepresence of object when not received.

BACKGROUND ART

[0002] As such an optical beam scanning type optical barrier apparatus,there is the apparatus disclosed for example in PCT InternationalPublication No. WO97/33186, and this will be briefly described.

[0003] In FIG. 2 of PCT International Publication No. WO97/33186, alaser beam generating means and a laser scanning means are arranged onone side of a detection area, and an array light receiving elements isarranged on the other side. In this apparatus, a laser beam generated bythe laser beam generating device is projected onto the laser scanningdevice, and the laser scanning device reflects the laser beam so as toscan an area including the detection area. If an object is not presentinside the detection area, the laser beam is received by the lightreceiving element array. If an object is present inside the detectionarea, the laser beam is blocked by the object so that the lightreceiving element positioned in the shadow of the object within thelight receiving element array does not receive the laser beam. Thedeficiency of light reception output signal from the light receivingelement array, which occurs at this time, is detected by a signaldeficiency detecting means, thus notifying of the presence of object.

[0004] Furthermore, in FIG. 3 and FIG. 6 of PCT InternationalPublication No. WO97/33186, there is disclosed a construction which usesa reflecting mirror.

[0005] In FIG. 3, the construction is such that a laser beam generatingdevice, a laser scanning device and a light receiving element array arearranged on the same side, and a concave reflecting mirror is arrangedon the other side. A laser beam generated by the laser beam generatingdevice is scanned at a predetermined spread angle by the laser scanningdevice, and projected onto the concave reflecting mirror arranged on theother side. The laser beams reflected by the concave reflecting mirrorare passed through a detection area as mutually parallel beams to bedirected towards the light receiving element array. Furthermore, in FIG.6, the construction is such that the light receiving element array ofFIG. 3 is replaced with a single light receiving element, and theposition of the laser scanning device and the shape and position of theconcave reflecting mirror are adjusted so that the reflected light ofthe concave reflecting mirror is focused onto the single light receivingelement.

[0006] However, with the abovementioned optical beam scanning typeoptical barrier apparatus, in the constructions of FIG. 2 and FIG. 3,since a light receiving element array is used, it is necessary to adjustlight reception directional characteristics of the light receivingelement array with respect to each of the elements. Furthermore, a lightreceiving circuit is needed for each of the respective light receivingelements, and hence there is a problem in that cost reduction isdifficult.

[0007] Furthermore, with the construction of FIG. 6, the light receivingelement is only one, and hence the cost can be reduced compared to FIG.2 and FIG. 3. However there is a problem in that there exists an areawhere the object detection is not possible, and the detection area thusbecomes narrow.

[0008] The present invention addresses the abovementioned problems withthe object of providing an optical barrier apparatus enabling of costreduction without narrowing the detection area.

DISCLOSURE OF THE INVENTION

[0009] In order to achieve the aforementioned object, an optical barrierapparatus according to the present invention comprises a first andsecond units facing each other with a detection area therebetween, eachof the first and second units comprising: optical beam generating means,optical beam scanning means for reflecting an optical beam generated bythe optical beam generating means so as to scan an area containing thedetection area, optical beam reflecting means for reflecting a scanningbeam incident from the optical beam scanning means via the detectionarea by turning back at approximately 180 degrees, light receiving meansarranged in the vicinity of the optical beam scanning means forreceiving a reflection beam from the optical beam reflecting means, andsignal deficiency detecting means for detecting the presence/absence ofa deficiency of output signal of the light receiving means andgenerating a notification output for object absence at the time of nodeficiency, wherein the optical beam scanning means and the lightreceiving means of the first unit and the optical beam scanning meansand the light receiving means of the second unit are arranged on eitherside of the detection area at approximately diagonal positions.

[0010] With such a construction, the optical beam generated from theoptical beam generating means is reflected and scanned by the opticalbeam scanning means. If an object is present in the detection area, thescanning beam does not reach the optical beam reflecting means so thatan optical beam at a predetermined level or above is not received by thelight receiving means. If an object is not present in the detectionarea, the scanning beam is reflected by the optical beam reflectingmeans and the light receiving means receives a reflection beam at apredetermined level or above. The signal deficiency detecting means, ifan output level of the light receiving means is at the predeterminedlevel or above, generates a notification output for object absence. Thistype of object detection is respectively performed in the first unit andsecond unit. Moreover, since the optical beam scanning means and lightreceiving means of the first unit, and the optical beam scanning meansand light receiving means of the second unit are arranged at diagonalpositions on either side of the detection area, the area where objectdetection is possible becomes a rectangular shape. As a result, thenumber of light receiving means can be reduced, costs can be reduced,and the detection area becomes rectangular so that the detection areacan be widened.

[0011] The construction may be such that there is provided synchronousdrive means for synchronizing the two optical beam scanning means of thefirst and second units with respect to each other so that when ascanning beam direction on the first unit side is a diagonal direction,a scanning beam direction on the second unit side is also a diagonaldirection. Then, when a scanning beam direction of one unit is adiagonal direction where it is easy for an optical beam from the otherunit to be erroneously received, if an object is present on an opticalaxis of an optical beam from the one unit, the scanning beam is blockedby the object so that erroneous notification attributable to receptionof the scanning beam of the other unit can be prevented.

[0012] Moreover, the construction may be such that there is providedselection drive means for selectively driving the first and second unitsso that object detection operations of the first unit and second unitare not performed at the same time. Since when one unit is being driventhe other unit is stopped, erroneous notification attributable toreception of the scanning beam of the other unit can be prevented.

[0013] Furthermore, the construction may be such the emissionwavelengths of optical beams respectively generated from the respectiveoptical beam generating means of the first unit and second unit are madedifferent from each other. Moreover, the construction may be such thatblinking frequencies of reflection beams respectively reflected fromeach optical beam reflecting means of the first unit and second unit aremade different from each other. In this case also, since the opticalbeam of the own unit and the optical beam of the other unit can bedistinguished, erroneous notification attributable to reception of thescanning beam of the other unit can be prevented.

[0014] Moreover, the construction may be such that each signaldeficiency detecting means verifies that a light reception output fromthe light receiving means is one based on a reflection beam from theoptical beam reflecting means, to generate a notification output forobject absence.

[0015] With such a construction, since it becomes possible todistinguish between the reflection light from the optical beamreflecting means and the light reflected by the object, then even in thecase where the reflectance of the object is high so that the lightreception level of reflection light from the object is equal to or abovea predetermined level, or the case where the object is near the lightreceiving means so that the light reception level of irregularlyreflected light from the object is equal to or above a predeterminedlevel, erroneous notification can be prevented.

[0016] Furthermore, the construction may be such that scanningverification means for verifying that the scanning beam is scannedwithin a range of the area including the detection area is provided ineach unit.

[0017] With such a construction, it becomes possible to verify with thescanning verification means, that the scanning beam is normally scanningthe detection area. Therefore, in the case where this construction isused as a safety ensuring facility for a machine, reliability for theoptical barrier apparatus can be improved.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018]FIG. 1 is a schematic configuration diagram of a first embodimentof an optical barrier apparatus according to the present invention.

[0019]FIG. 2 is a configuration diagram of a unit of the firstembodiment.

[0020]FIG. 3 is an operation time chart of the first embodiment.

[0021]FIG. 4 is a diagram of a retroreflector.

[0022]FIG. 5 is an explanatory diagram of problems of an optical barrierapparatus of the present invention, FIG. 5A being a diagram showing acondition where one scanning beam is blocked by an object while anotherscanning beam is received, and FIG. 5B being a time chart showing alight reception output condition for the case of FIG. 5A.

[0023]FIG. 6 is a configuration diagram of the main parts of a secondembodiment of the present invention.

[0024]FIG. 7 is a diagram for explaining an operation of the secondembodiment.

[0025]FIG. 8 is a configuration diagram of the main parts of a thirdembodiment of the present invention.

[0026]FIG. 9 is a configuration diagram of the main parts of a fourthembodiment of the present invention, FIG. 9A being a diagram of thescanning conditions of a scanning beam, and FIG. 9B being aconfiguration diagram of a signal deficiency detection circuit.

[0027]FIG. 10 is an operation time chart of the fourth embodiment.

[0028]FIG. 11 is a configuration diagram of the main parts of a fifthembodiment of the present invention.

[0029]FIG. 12 is a configuration diagram of the main parts of a sixthembodiment of the present invention, FIG. 12A being a configurationdiagram of a reflector array, and FIG. 12B being a time chart of a lightreception output of each unit.

[0030]FIG. 13 is a diagram showing an example of another method forpreventing direct reception of a beam from another unit, FIG. 13A beinga top view of the optical barrier apparatus, and FIG. 13B being a frontview of the optical barrier apparatus.

[0031]FIG. 14 is a configuration diagram of the main parts of a seventhembodiment of the present invention.

[0032]FIG. 15 is an operation time chart of the seventh embodiment.

[0033]FIG. 16 is a configuration diagram of the main parts of an eighthembodiment of the present invention.

[0034]FIG. 17 is a configuration diagram of the main parts of a ninthembodiment of the present invention, FIG. 17A being a configurationexample for receiving a scanning beam except for its own, and FIG. 17Bbeing a configuration diagram of a circuit of a unit.

[0035]FIG. 18 is an operation time chart of the ninth embodiment.

[0036]FIG. 19 is a configuration diagram of a scanning verificationsection.

[0037]FIG. 20 is a block diagram of the scanning verification section.

[0038]FIG. 21 is an operation time chart of the scanning verificationsection.

[0039]FIG. 22 is a configuration diagram of the main parts for the casewhere the scanning verification section is applied to the opticalbarrier apparatus of the present invention.

[0040]FIG. 23 is a perspective view of a semiconductor galvano-mirror.

BEST MODE FOR CARRYING OUT THE INVENTION

[0041] Hereunder is a description of embodiments of an optical barrierapparatus according to the present invention based on the appendeddrawings.

[0042]FIG. 1 shows a schematic configuration of a first embodiment ofthe optical barrier apparatus according to the present invention.

[0043] In FIG. 1, the optical barrier apparatus according to thisembodiment comprises first and second units 10 and 20 facing each otheron either side of a detection area 1.

[0044] Each unit 10 and 20 comprises; an optical beam generating circuit11, 21 (shown in FIG. 2) serving as optical beam generating means, ascan mirror 12, 22 for reflecting an optical beam generated from theoptical beam generating circuit 11, 21 so as to scan the detection area1 at a predetermined spread angle and generate scanning beams BM1, BM2,a reflector array 13, 23 serving as optical beam reflecting means,having multiple reflectors 13-1 to 13-n, 23-1 to 23-n arranged in thevertical direction of the detecting area 1, for reflecting the scanningbeams BM1, BM2 incident via the detection area 1 by turning back atapproximately 180 degrees, a light receiving element 14, 24 serving aslight receiving means arranged in the vicinity of the scan mirror 12, 22for receiving reflection beams reflected by the reflector array 13, 23and incident via the detection area 1, and a signal deficiency detectioncircuit 15, 25 (shown in FIG. 2) serving as signal deficiency detectingmeans for detecting the presence/absence of a deficiency of an outputsignal of the light receiving element 14, 24 to generate a notificationoutput for object absence when there is no deficiency.

[0045] A detection area by one unit of the optical barrier apparatus ofthis embodiment is of approximate triangular shape with the scan mirror12 (scan mirror 22) on the first unit 10 (second unit 20) side andopposite end reflectors 23-1 and 23-n (reflectors 13-1 and 13-n) on thesecond unit 20 (first unit 10) as apexes. Furthermore, with the opticalbarrier apparatus of this embodiment, the scan mirror 12 and the lightreceiving element 14 of the first unit 10, and the scan mirror 22 andthe light receiving element 24 of the second unit 20 are arrangeddiagonally as shown in FIG. 1 on either side of the detection area 1.Therefore with the optical barrier apparatus of this embodiment, anapproximate rectangular shape detection area 1 can be obtained as inFIG. 1.

[0046] Here, the optical beam to be used may be of narrowdirectionality, for example, a laser beam is desirable. However, anoptical beam where light rays generated using a LED or the like as alight emission element are given narrow directionality with a lensoptical system or the like may also be used.

[0047] Referring to FIG. 2, the configuration of the first unit 10 willbe described in detail.

[0048] In FIG. 2, the optical beam generating circuit 11 generates anoptical beam from a light emitting element 11B by means of a lightemitting element drive circuit 11A. By making the optical beam as a highfrequency pulse emission, the influence of disturbance light such assunshine can be effectively suppressed. For example, the light emittingelement drive circuit 11A is made an oscillating circuit which uses forexample an astable multivibrator, to blink the light emitting element11B with an oscillation output from the astable multivibrator.

[0049] The scan mirror 12 reflects the optical beam incident from thelight emitting element 11B to scan the same in a range of thepredetermined spread angle. The scan mirror 12 is rotated at apredetermined period about a rotation axis 12 a as shown by the arrow inthe figure by means of a scan mirror drive circuit 16, so that thescanning beam BM1 reaches to each reflector 23-1 to 23-n of the otherunit 20. The scan mirror 12 and the scan mirror drive circuit 16constitutes optical beam scanning means.

[0050] The signal deficiency detection circuit 15 comprises a lightreception circuit 17, a comparator 18, and a pulse deficiency detectioncircuit 19. The light reception circuit 17 amplifies the light receptionsignal from the light receiving element 14. The comparator 18 comprisesa rectifying circuit 18A for performing an envelope detection on anoutput signal Sa from the light reception circuit 17, and a thresholdvalue computing circuit 18B for computing a threshold value for arectified output S1 from the rectifying circuit 18A, and when the levelof the rectified output S1 of the signal Sa is equal to or above athreshold value Vt1, outputs Sb=1 (logic value 1), while when the levelof the rectified output S1 is less than the threshold value Vt1, outputsSb=0 (logic value 0). The pulse deficiency detection circuit 19comprises an off-delay circuit 19A having a capacitor C, a diode D, anda threshold value computing circuit 19 a having a threshold value Vt2,for delaying the falling of the signal Sb by a predetermined off-delaytime Tof, and an on-delay circuit 19B for delaying the rising of theoutput S2 from the off-delay circuit 19A by a predetermined on-delaytime Ton.

[0051] The second unit 20 also has the same construction as that of thefirst unit 10.

[0052] Next is a description of an object detection operation of thepresent embodiment, based on a time chart of FIG. 3.

[0053] A high frequency optical beam is generated from the lightemitting element 11B by the oscillating output from the light emittingdrive circuit 11A. The optical beam is reflected by the scan mirror 12so as to cross the detection area 1, and is incident on the second unit20 as the scanning beam BM1. The scan mirror 12 is rotated at thepredetermined period by the scan mirror drive circuit 16, so that thelight projection direction of the scanning beam BM1 for scanning thedetection area 1 changes by every moment, to thereby scan the detectionarea 1 with the scanning beam BM1. The scanning beam BM1 passes throughthe detection area 1 if an object 30 (shown in FIG. 2) is not present,and is successively incident on the reflectors 23-1 to 23-n of thesecond unit 20, and is then reflected so as to turn back atapproximately 180 degrees (for convenience of explanation, in thefigure, the scan mirror 12 and the light receiving element 14 are shownapart from each other with an angle between the scanning beam BM1 andscanning beam BM1′), and the scanning beam BM1′ having passed throughapproximately the same path as the scanning beam BM1 is received by thelight receiving element 14.

[0054] A light reception output from the light receiving element 14 isamplified by the light reception circuit 17 and input to the comparator18 as the signal Sa. The signal Sa input to the comparator 18 isenvelope detected by the rectifying circuit 18A and input to thethreshold value computing circuit 18B as the signal S1. The thresholdvalue computing circuit 18B compares the level of the signal S1 with theinput threshold value Vt1, and if the signal S1 is equal to or aboveVt1, generates Sb=1 (logic value 1), while if the signal S1 is a lowerlevel than Vt1, generates Sb=0 (logic value 0). The output signal Sbfrom the comparator 18 is input to the off-delay circuit 19A inside thepulse deficiency detection circuit 19. The off-delay circuit 19A outputsa signal S2=1 coping with the rising (0→1) of the signal Sb, butcontinues the signal S2=1 for an off-delay time Tof without coping withthe falling (1→0) of the signal Sb. Since the off-delay time Tof is setto be longer than the period where there is no light reception of thereflection beam BM1′ produced at normal times, then if at normal timesthe object 30 is not present, then as shown in FIG. 3, the signal S2=1is continued. If this continuous time is equal to or more than theon-delay time Ton of the on-delay circuit 19B, then Z1=1 is generatedfrom the on-delay circuit 19B to notify of the absence of object 30.

[0055] As shown in FIG. 2, in the case where the object 30 is present inthe detection area 1, since the scanning beam BM1 is blocked by theobject 30, the reflection beam BM1′ from the reflector positioned in theshadow of the object 30 does not appear. In this case, even if the lightirregularly reflected by the object 30 is received by the lightreceiving element 14, the light reception level thereof is small.Consequently, the level of the signal S1 is a lower level than thethreshold value Vt1 of the threshold value computing circuit 18B, sothat the output from the comparator 18 becomes Sb=0. If this Sb=0condition is continued for the off-delay time T of or more, signal S2=0results, and the output from the on-delay circuit 19B becomes Z1=0, thusnotifying of the presence of object 30.

[0056] Since the on-delay time Ton of the on-delay circuit 19B is set tobe longer than one scanning period of the scanning beam BM1, Z1=0generated once from the signal deficiency detection circuit 15 is heldthereafter for at least more than one scanning period of the scanningbeam BM1, and Z1=0 is continued provided S2=0 is continued in the nextand subsequent scanning periods.

[0057] Also in the second unit 20, an operation similar to the above isperformed. The notification output from the first unit 10 is made Z1,and a notification output from the second unit 20 is made 79, and bothoutputs Z1 and Z2 from the two units 10 and 20 are input to logicalproduct computation circuits, and the logical product computationresults becomes the final notification output Z for the optical barrierapparatus. As a result, the first unit 10 monitors the lower sidetriangular area of the detection area 1 of FIG. 1, while the second unit20 monitors the upper side triangular area of the detection area 1, sothat in total, a rectangular shape detection area 1 can be monitored.

[0058] With the abovementioned embodiment, the construction is such thatthe respective reflectors 13-1 to 13-n, and 23-1 to 23-n are arrangedwith a gap provided. Therefore, the reflection beam BM1′ becomesintermittent so that the output signal Sb from the comparator 18 becomesa pulse signal. In the case where the reflectors 13-1 to 13-n and 23-1to 23-n are arranged in succession without a gap, the signal Sb is not apulse signal but becomes a continuous signal. In this case also, thepresence/absence of object can be monitored by adopting the signaldeficiency detection circuit of FIG. 2. Moreover, also if DC light isused for the optical beam rather than the high frequency pulse, only therectifying circuit 18A of the comparator 18 becomes unnecessary, whilethe rest can be applied as is.

[0059] With the optical barrier apparatus of this construction, only onelight receiving element need be provided for each unit 10 and 20, sothat the number of light receiving elements and light receiving circuitscan be significantly reduced, enabling a reduction in cost. Furthermore,the area between the units 10 and 20 can be monitored as a rectangularshape.

[0060] In the case where each reflector 13-1 to 13-n and 23-1 to 23-n isa flat plate, if the spacing between the units 10 and 20 (that is thespacing between the scan mirrors 12, 22 and the reflector array 23,13)is changed, then a deviation such as in the end point positions of thereflection beams occurs. Therefore in the case where the distancebetween the units 10 and 20 is changed, then each time, angle adjustmentof each reflector 23-1 to 23-n and 13-1 to 13-n is necessary. However,if for the reflectors of each reflector array 13 and 23 a retroreflectoras shown in FIG. 4 is used, this has the advantage that the scanningbeam can be reflected back at 180 degrees, so that even if the spacingbetween the units 10 and 20 is changed, angle adjustment of thereflectors becomes unnecessary.

[0061] Incidentally, in the case of the optical barrier apparatus of thepresent invention where, as shown in FIG. 1, two units 10 and 20 arecombined, the scanning range of the scanning beams is previouslyadjusted so that the scanning beam from one unit is not received by thelight receiving element of the other unit. However, such a situation mayarise where due to a change in the environment or the like, anotherscanning beam is received rather than the beam which should be received.For example, there is the case such as where the scanning beam BM2 fromthe scan mirror 22 of the second unit 20 is erroneously directlyreceived by the light receiving element 14 of the first unit 10.

[0062] In such a case the following problem arises.

[0063] That is to say, there is the object 30 as shown in FIG. 5A. Inthis case, as mentioned before, the scanning beam BM1 on the first unit10 side is blocked, so that the reflection beam from the reflectorpositioned in the shadow of the object 30 is not received by the lightreceiving element 14, and as shown by the dotted line in FIG. 5B, apulse deficiency occurs in the light reception output for the scanningbeam BM1. If at a timing where this pulse deficiency is covered up, thescanning beam BM2 from the scan mirror 22 on the second unit 20 side isdirectly received by the light receiving element 14 so that a lightreception pulse is generated, the actual light reception output from thelight receiving element 14, as shown in FIG. 5B becomes a signal withouta pulse deficiency, similar to that at normal times. As a result,although the object 30 is present, absence of object 30 is notified.

[0064] Second to sixth embodiments for solving this problem are shownhereunder.

[0065] The second embodiment shown in FIG. 6 is constructed such thatthe scan mirror drive circuits 16 and 26 of the first and second units10 and 20 are synchronized by a synchronous signal from a synchronoussignal generating circuit 40 being synchronous drive means. That is, asshown in FIG. 7, the construction is such that the rotating operationsof the scan mirrors 12 and 22 are synchronized with each other so thatwhen the direction of the scanning beam BM1 on the first unit 10 side isa diagonal direction, the direction of the scanning beam BM2 on thesecond unit 20 side is also a diagonal direction. In FIG. 6, otherconstruction is the same as for FIG. 2 and diagrams thereof are omitted.

[0066] The operation of the second embodiment will now be described.

[0067] When the scanning beam BM1 on the first unit 10 side is directedtowards the reflector 23-1, the scanning beam BM2 on the second unit 20side is directed towards the reflector 13-n. At this time, if the object30 is not present on the optical axis, there is a possibility that thescanning beam BM2 is received by the light receiving element 14 on thefirst unit 10 side, and the scanning beam BM1 is received by the lightreceiving element 24 on the second unit 20 side. However, reception ofthe scanning beam due to object absence is no problem from the point ofsafety.

[0068] On the other hand, if as shown by the shaded portion in thefigure, the object 30 is present on the optical axis, the scanning beamsBM1 and BM2 are both blocked by the object 30 so that these do not reachthe light receiving elements 24 and 14. Moreover, due to the presence ofobject 30, the scanning beams BM1 and BM2 do not both reach thereflectors 23-1 and 13-n. Therefore there is no light reception of thereflection beam. Consequently, neither of the light receiving elements14 and 24 generates a light reception output, and the presence of object30 is thus detected. Therefore, the presence of object 30 can bedetected without error.

[0069]FIG. 8 shows the third embodiment of the present invention being adifferent construction example.

[0070] This embodiment is of a construction where the first and secondunits 10 and 20 are operated alternately by time sharing so as not toperform mutually duplicate object detection operations. In this way,while in one unit the scanning beam is being generated to perform objectdetection, the scanning beam of the other unit is not generated.Therefore the erroneous light reception described in FIG. 5 does notarise.

[0071] In FIG. 8, with the present embodiment, the construction is addedwith a selection circuit 50 serving as selection drive means, forgenerating selection signals E1 and E2 for selecting the unit to bedriven, and a signal processing circuit 51 serving as signal selectionmeans, for processing the light reception output.

[0072] The selection circuit 50 generates the selection signals E1 andE2 complementary to each other which do not simultaneously become logicvalue 1, and respectively supplies the selection signal E1 to the lightemitting element drive circuit 11A of the optical beam generatingcircuit 11 of the first unit 10, and supplies the selection signal E2 tothe light emitting element drive circuit 21A of the optical beamgenerating circuit 21 of the second unit 20.

[0073] The signal processing circuit 51 is constructed to comprise afirst logical product computing circuit 52 for computing a logicalproduct of the output from the signal deficiency detection circuit 15 ofthe first unit 10 and the selection signal E1, a second logical productcomputing circuit 53 for computing a logical product of the output fromthe signal deficiency detection circuit 25 of the second unit 20 and theselection signal E2, and a logical sum computing circuit 54 forcomputing a logical sum of the outputs from both logical productcomputing circuits 52 and 53, so that the output from the logical sumcomputing circuit 54 is an object detection output Z.

[0074] The operation will now be described.

[0075] When the selection signal E1 of the selection circuit 50 is logicvalue 1, an optical beam is generated from the light emitting element11B of the first unit 10. At this time, the selection signal E2 is logicvalue 0, and the detection operation of the second unit 20 is stopped.On the other hand, when the selection signal E2 is logic value 1, anoptical beam is generated from the light emitting element 21 B of thesecond unit 20. At this time, the selection signal E1 is logic value 0,and the detection operation of the first unit 10 is stopped. Since theselection signals E1 and E2 do not simultaneously become logic value 1,the scanning beams BM1 and BM2 are not generated simultaneously.

[0076] The signal processing circuit 51, when the selection signal E1 islogic value 1, that is, only when the scanning beam BM1 is beinggenerated, transmits the output Z1 from the signal deficiency detectioncircuit 15 to the logical sum computing circuit 54 as the output fromthe logical product computing circuit 52, to make the output Z1effective. Moreover, when the selection signal E2 is logic value 1, thatis, only when the scanning beam BM2 is being generated, the signalprocessing circuit 51 transmits the output Z2 from the signal deficiencydetection circuit 25 to the logical sum computing circuit 54 as theoutput from the logical product computing circuit 53, to make the outputZ2 effective.

[0077] With such a construction, even if the scanning beam BM1 on thefirst unit 10 side is directly received by the light receiving element24 on the second unit 20 side, or even if the scanning beam BM2 on thesecond unit 20 side is directly received by the light receiving element14 on the first unit 10 side, the outputs from the logical productcomputing circuits 52 and 53 do not become logic value 1 so that when anobject is present, an erroneous output of object absence due toerroneous reception of a scanning beam on the other unit side is notgenerated.

[0078] If the scanning beams BM1 and BM2 are processed so as not to bereceived by the light receiving elements 24 and 14 on the other unitsides, respectively, then in the period where the scanning beam BM1being generated, the output from the signal deficiency detection circuit25 becomes Z2=0, while in the period where the scanning beam BM2 isbeing generated, the output from the signal deficiency detection circuit15 becomes Z1=0. Therefore, in the signal processing circuit 51, the twological product computing circuits 52 and 53 may be omitted, the logicalsum computing circuit 54 only being sufficient, so that there is also noneed to supply the selection signals E1 and E2.

[0079]FIG. 9A and FIG. 9B show the fourth embodiment of the presentinvention being yet another construction example.

[0080] The fourth embodiment of the present invention shown in FIG. 9 isof a construction where the light emission frequency of the optical beamgenerated by the light emitting element 11B on the first unit 10 side isdifferent from the light emission frequency of the optical beamgenerated by the light emitting element 21B on the second unit 20 side.

[0081] As shown in FIG. 9A, with this embodiment, the light emissionfrequency of the optical beam from the light emitting element 11B ismade f1, and the light emission frequency of the optical beam from thelight emitting element 21B is made f2 (f1≠f2).

[0082]FIG. 9B shows the construction of the signal deficiency detectioncircuit of this embodiment.

[0083] In the figure, a light reception circuit 17′ of the signaldeficiency detection circuit 15 of the first unit 10 has an amplifyingcircuit 61, and a band pass filter 62 of a central frequency fi servingas signal extraction means for extracting only scanning beam signalcomponents of its own unit. The signal deficiency detection circuit 25of the second unit 20, with the exception that the central frequency ofthe band pass filter inside the light receiving circuit is f2, is thesame as that of the first unit 10 side, and hence this is omitted fromthe figure. Other construction is the same as for the first embodimentshown in FIG. 2.

[0084] The operation of the first unit 10 side will now be describedwith reference to a time chart of FIG. 10.

[0085] When the light receiving element 14 receives the reflection beam,the light reception circuit 17′ amplifies the output signal from thelight receiving element 14 in the amplifying circuit 61, and generates alight reception signal S3. The signal S3 is input to the band passfilter 62 to be frequency detected. The band pass filter 62 outputs theoptical beam of light emission frequency f1 to be received by the lightreceiving element 14 with practically no attenuation. In this case, thelevel of the input signal S3 to the band pass filter 62 and the outputsignal Sa is Sa≈S3. The signal Sa is input to the comparator 18 to belevel detected similarly to the case of the first embodiment of FIG. 2.If the rectified output S1 level of the signal Sa is equal to or abovethe threshold value Vt1, Sb=1 is generated, while if the signal S1 levelis a lower level than Vt1, Sb=0 is generated.

[0086] The output signal Sb from the comparator 18 is input to theoff-delay circuit 19A inside the pulse deficiency detection circuit 19,and if the reflection beam BM1′ of frequency f1 is normally received,the signal S2=1 is continued, and when the continuation time becomes theon-delay time Ton of the on-delay circuit 19B or more, Z1=1 is generatedfrom the on-delay circuit 19B to thus notify of the absence of object.If there is an object inside the detection area 1, a pulse deficiency asshown by the dotted line in FIG. 10 is produced, and if the signal Sb=0is continued for the off-delay time Tof or more, S2=0 is generated andthe output Z1 from the on-delay circuit 19B becomes Z1=0, thus notifyingof the presence of object.

[0087] On the other hand, even if the optical beam BM2 of frequency f2on the second unit 20 side, which is not to be received by the lightreceiving element 14, is received by the light receiving element 14 sothat a signal S3 is generated, this signal S3 is frequency detected bythe band pass filter 62 and removed. That is, the attenuationcharacteristic of the band pass filter 62 is set so that even if thesignal S3 becomes a maximum level due to the light reception of theoptical beam BM2 of emission frequency f2, the signal S1 level as shownin the figure becomes a level lower than the threshold value Vt1. As aresult, the signal Sb=1 is not generated, so that the problem due toerroneous light reception of the scanning beam from the other unit canbe avoided.

[0088] Furthermore, as with the fifth embodiment of the presentinvention shown in FIG. 11A, the construction may be such that thepitches L1 and L2 of the reflectors 13-1 to 13-n and 23-1 to 23-m in thereflector array 13 of the first unit 10 and the reflector array 23 ofthe second unit 20 is made different. In this case, as shown in FIG.11B, the frequencies of the envelope detection signals of the respectivelight reception signals of the light receiving elements 14 and 24 in onescanning period, that is, the blinking frequencies of the reflectionbeams, become different. The signal deficiency detection circuit of thisembodiment is the same as the circuit of FIG. 9B. However, the centralfrequencies f1 and f2 of the band pass filters 62 become the blinkingfrequencies of the reflection beams.

[0089] Moreover, as with the sixth embodiment of FIG. 12, also if theconstruction is such that masks 13 a and 23 a with widths L1 and L2 areattached at predetermined spacing on single plate reflectors 13 a and 23a, so that substantially a plurality of reflecting sections (in thefigure shown as reflectors 13-1 to 13-n and 23-1 to 23-m) are providedto make the reflector arrays 13 and 23, the operation and effect similarto those of FIG. 11 can be obtained.

[0090] Here, if reflectors (or reflecting sections) of the two units 10and 20 are arranged in the same number, and the scanning speeds of thescan mirrors 12 and 22 are made different, the blinking frequency of thelight reception output in the one scanning period of the two units 10and 20 becomes different. Hence the operation and effect similar tothose for the cases of FIG. 11 and FIG. 12 can be obtained. In the casesof FIG. 11 and FIG. 12, also if DC light is used in the scan beams BM1and BM2, the influence from disturbance light such as from sunshine canbe suppressed.

[0091] According to the constructions of the fifth and sixth embodimentsin FIG. 11 and FIG. 12, an error as described later where the lightreception strength of the irregularly reflected light from the object islarge as if this is regarded just as reception light from the reflector(or reflecting section), can be avoided.

[0092] That is, in the fifth and sixth embodiments, the reflection beamsfrom the reflector arrays 13 and 23 become blinking lights atpredetermined frequencies f1 and f2 in the respective one scanningperiods. On the other hand, when irregularly reflected light is receivedfrom the object, this type of blinking light is not generated.Consequently, light from the reflector array and irregularly reflectedlight can be discriminated, and if irregularly reflected light ispresent, the output from the signal deficiency detection circuit becomeslogic value 0.

[0093] As a method for discriminating between the scanning beams BM1 andBM2, the wavelength of the scanning beams BM1 and BM2 may be madedifferent. In this case, wavelength filters for passing only scanningbeams BM1 and BM2 of respective wavelengths which should actually bereceived, and strength attenuating or blocking off scanning beams BM2and BM1 of wavelengths which should not to be received, may be providedon the light receiving surfaces of the respective light receivingelements 14 and 24 of the units 10 and 20. In this way, erroneous lightreception of scanning beams which should not to be received can beprevented. In the signal deficiency detection circuits 15 and 25 on thelight receiving side, the construction of FIG. 2 may be used.

[0094] By devising a geometrical arrangement of detection area ofapproximately triangular shape in each unit, the problem of erroneousreception of scanning beam from the other unit can be resolved. Ingeneral, as shown in FIG. 13A and FIG.13B, the respective scan mirrorsand light receiving elements of the units 10 and 20 may be arranged sothat the face of the triangular detection area 1A of the first unit 10,and the face of the triangular detection area 1B of the second unit 20are not in the same plane. By arranging in this manner, direct receptionof the scanning beam from the other unit can be prevented. FIG. 13A is aplan view and FIG. 13B is a front view.

[0095] Incidentally, in the case of an object with good reflectance (forexample a mirror or the like), it is likely that, depending on theposition of the object inside the detection area 1, the scanning beam isreflected back at 180 degrees by the object without scattering so thatlight of sufficient strength is received by the light receiving element.Furthermore, in the case where the object is present near the scanmirror and the light receiving element, then even if the scanning beamis scattered and reflected by the object, it is possible for thisscattered light to be received by the light receiving element at astrength of the degree to erroneously show object absence.

[0096] An embodiment to resolve this problem is shown below.

[0097] In a seventh embodiment shown in FIG. 14, the construction issuch that there is provided a function for verifying that a reflectionbeam received by a light receiving element is one which is reflected bya reflector. The basic construction of FIG. 14 is known for example fromJapanese Unexamined Patent Publication No. 10-38194.

[0098] In FIG. 14, with the present embodiment, at least one of thereflector arrays 13 is a specific reflector 13-P (P=1 to n), and thereflector 13-P has one end thereof rotatably supported by a pivot 71. Anelectrostrictive element 72 is attached to the other end as modulationmeans. The electrostrictive element 72 is AC driven at a frequency f3 bya drive circuit (not shown in the figure). On the other hand, in thesignal deficiency detection circuit 15, to the construction of FIG. 2there is newly added an envelope detection circuit 73, a pulsedeficiency detection circuit 74, and a logical product computing circuit75. The envelope detection circuit 73 is a rectifying circuit whichenvelope detects the output Sb from the comparator 18 and outputs Sc=1only when the input signal frequency is a high frequency signal equal toor above f3. The pulse deficiency detection circuit 74 incorporates anoff-delay circuit and an on-delay circuit, and detects a pulsedeficiency of the output Sc from the envelope detection circuit 73.However, the off-delay time Tof1 of the off-delay circuit of the pulsedeficiency detection circuit 74 is longer than this period for theoutput Sc=0 from the envelope detection circuit 73 which is normallygenerated and shorter than two periods for where Sc=1 is generated.Furthermore, the on-delay time of the on-delay circuit is set to be atleast longer than the Sc=1 generating period. The second unit 20 side isalso of the same construction.

[0099] Hereunder is a description of the operation with reference to atime chart of FIG. 15.

[0100] At the time of a monitoring operation, the reflector 13-P is ACdriven by the electrostrictive element 72 at the frequency f3. When avoltage is not applied, the reflector 13-P becomes the condition shownby the solid line in FIG. 14. In this condition, the scanning beam BM1is reflected in the direction of the light receiving element 14 andreceived thereby. When a voltage is applied, the reflector 13-P becomesthe condition shown by the dotted line in FIG. 14. In this condition,the scanning beam BM1 is not reflected in the direction of the lightreceiving element 14 and is thus not received. Consequently, if thedrive frequency of the electrostrictive element 72 is f3, the lightreception output from the light receiving element 14 based on receptionof the reflection beam from the reflector 13-P, repeats alternately atthe frequency f3 between reception and non reception. As a result,regarding the output signal Sa from the light reception circuit 17 basedon reception of the reflection beam from the reflector 13-P, as shown inFIG. 15, the signal of frequency f1 becomes a waveform with theamplitude modulated at frequency f3. This gives the relationship(reception period of reflection beam from reflector 13-P)>1/f3>1/f1.

[0101] Since the scanning beam BM1 is scanned at a predetermined period,then at normal times, the modulating signal due to the reflector 13-Palso is periodically generated as shown in FIG. 15. Of the outputsignals Sb from the comparator 18, the signal of frequency f3 isdetected by the envelope detection circuit 73 and output as Sc=1. IfSc=1 is periodically generated, the pulse deficiency detection circuit74 continues to generate an output Y1=1. Moreover, in the case where thereflection beam from the reflector 13-P is not received, the signal offrequency f3 is not generated in the signal Sb. Therefore, the outputfrom the envelope detection circuit 73 becomes Sc=0, and a pulsedeficiency is produced as shown by the dotted line in FIG. 15. As aresult, the output from the pulse deficiency detection circuit 74becomes Y1=0. This signal Y1 and the output Z1 from the pulse deficiencydetection circuit 19 are subjected to logical product computation by thelogical product computing circuit 75, and the resultant output ZYbecomes a signal indicating the presence/absence of object on the firstunit 10 side.

[0102] Also in the case where the abovementioned modulation means suchas an electrostrictive element is attached to a plurality of reflectorsof the reflector array, the circuit configuration of FIG. 14 can beused. Moreover, if the construction is such that the modulation means isattached to all of the reflectors to modulate the scanning beam at thesame frequency f3, then even when the optical beam is direct currentlight, this becomes alternating current light of frequency f3 whenreceived. Therefore, it is not necessary to make the emission frequencyf1. Furthermore, if the modulation means is attached to all thereflectors on the second unit 20 side so that the scanning beam BM1 ismodulated at frequency f3, and similarly on the first unit 10 side sothat the scanning beam BM2 is modulated at a frequency different fromf3, then as with the fourth embodiment of FIG. 9, the problem oferroneous light reception of scanning beam by another unit side can alsobe resolved. In this case, the circuit of FIG. 9B may be used in thereception circuit of the signal deficiency detection circuit.

[0103] Next an eighth embodiment of the present invention being anotherconstruction example is shown in FIG. 16 and will be described. Thisembodiment is applied to the case where the optical beam reflectingmeans is constructed at a plurality of divided reflecting areas, thatis, where a reflecting portion and a non reflecting portion are multiplyarranged alternately. For example, this embodiment is applied to thecase where this is constructed with a plurality of reflectors, or thecase where a plurality of masks as shown in FIG. 11 and FIG. 12 areprovided. Here, the description is for the case where the reflectorarray comprises a plurality of reflectors.

[0104] In FIG. 16, there is provided a counting circuit 90 input withthe output Sb from the comparator 18 of the signal deficiency detectioncircuit 15 of FIG. 2, and the drive signal SD1 from the scan mirrordrive circuit 16, for counting the number of generations of the signalSb per one scanning period of the scan mirror 12. The construction issuch that an output Zc from the counting circuit 90 and the output Z1from the signal deficiency detection circuit 15 (the output from thepulse deficiency detection circuit 19) are computed by a logical productcomputation circuit 91, and an output from the logical productcomputation circuit 91 becomes a detection signal Z1 for objectpresence/absence.

[0105] In the case where as shown in FIG. 1, the reflector arrays 13 and20 comprise the plurality of divided reflectors 13-1 to 13-n and 23-1 to23-n, the number of pulses of the reflection beams received in onescanning period of the scanning beam is equal to the number ofreflectors of the reflector arrays 13 and 23. If an object is present,at least one or more reflection beams is not received, and hence thenumber of pulses of reflection beams is decreased. Furthermore, in orderto prevent the error where due to the large light reception strength ofthe irregularly reflected light from the object, it is considered thatthere is reception light, if the spacing of adjacent reflectors is setnarrow so that the irregularly reflected light from the smallest objectto be detected is continued for the amount of the reflected light fromtwo or more reflectors, the number of pulses of reflection beams isdecreased.

[0106] Regarding the operation, the counting circuit 90 counts thenumber of signals Sb input per one scanning period of the scan mirror 12based on the signal SD1, and compares this count value with a set valuepreviously set corresponding to the number of reflectors. If the countvalue coincides with the set value, the counting circuit 90 outputsZc=1. If the count value does not coincide with the set value, thecounting circuit 90 outputs Zc=0. The verification signal Zc of thispulse number and the output Z1 from the pulse deficiency detectioncircuit 19 are input to the logical product computation circuit 91, andan output Z of the computation result thereof becomes a detection signalfor object presence/absence.

[0107] The counting circuit used in this embodiment has a function thesame as the pulse deficiency detection circuit 19, since this counts thepulse number per one scanning period of the scan mirror. Therefore, thepulse deficiency detection circuit 19 in each of the aforementionedembodiments may be replaced by the counting circuit 90.

[0108] Furthermore, the method for detecting the frequency of the pulsesignal generated as signal Sb may also be adopted. As also mentioned inthe description for the aforementioned fifth and sixth embodiments, thereflected pulse light of frequency f1 to be received due to an objectabsence, if an object is present, does not occur while the object isbeing scanned by the scanning beam. That is, due to an object presence,the frequency of the reflected light becomes outside the frequency f1.Hence by performing frequency detection of the reception light signal,the presence/absence of object can be detected. The blinking frequencyof the reflected light for the units 10 and 20 may be the same, if forexample problems due to receiving scanning beam light from other unitsare not considered.

[0109] Regarding the frequency test, for example, the construction maybe such that, in FIG. 16, a band pass filter (central frequency f1) isprovided and the signal Sb input thereto, and the output therefrom inputto a separately provided comparator and subjected to threshold valuecomputation, and the output then input to the pulse deficiency detectioncircuit 19 (in this case, the counting circuit may naturally beomitted).

[0110] If the frequency of the signal Sb becomes outside f1 due to anobject presence, then as in FIG. 10, the filter output level drops tobecome lower than the threshold value of the comparator so that a pulsedeficiency occurs and the object presence can be detected.Alternatively, using the circuit of FIG. 9B with the emitted beam asdirect current light, the frequency of the reflection beam may bedetected.

[0111]FIG. 17A and FIG. 17B show a ninth embodiment of the presentinvention being yet another configuration example.

[0112] In FIG. 17, with this embodiment, as shown in FIG. 17A, theconstruction is such that reflectors Tp1 and Tp2 are separately providedso that when an optical beam other than that of the own unit, forexample the scanning beam BM2 of the second unit 20 side, is projectedin a predetermined direction, this optical beam BM2 is reflected so asto be received by the light receiving element 14 on the first unit 10side. To this end, as shown in FIG. 17B, the construction is such thaton the light reception side, in addition to the signal deficiencydetection circuit 15 of the construction of FIG. 9B, there is providedan other beam reception verification circuit 80 for verifying that thescanning beam BM2 of frequency f2 is being received at a predeterminedperiod by the light receiving element 14.

[0113] The other beam reception verification circuit 80 comprises a bandpass filter 81 with a central frequency f2, a comparator 82, a timingsignal generating circuit 83 for outputting a timing signal TM withinput of a scan mirror drive signal SD2 of the second unit 20 side, alogical product computing circuit 84, and a pulse deficiency detectingcircuit 85, and when the scanning beam BM2 is normally received by thelight receiving element 14 at a predetermined timing, generates anoutput V1=1.

[0114] The operation of the ninth embodiment will be described withreference to a timing chart of FIG. 18.

[0115] When a light reception output is generated from the lightreceiving element 14 on reception of the reflection beam, the lightreception signal S1 amplified by the amplifying circuit 61 isrespectively input to the band pass filters 62 and 81. As described forthe fourth embodiment of the FIG. 9, signals outside the frequency f1are attenuated by the band pass filter 62 and output to the comparator18 as the signal Sa, and level detected by the pulse deficiencydetection circuit 19. On the other hand, the band pass filter 81 of theother beam reception verification circuit 80 attenuates the signalsoutside the frequency f2 and outputs to the comparator 82 as a signalSa′. With this embodiment, the light receiving element 14 and theamplifying circuit 61 are not saturated even if the two scanning beamsBM1 and BM2 are simultaneously received by the light receiving element14.

[0116] The timing signal generating circuit 83 of the other beamreception verification circuit 80 outputs a timing signal TM with inputof a drive signal SD2 indicating that the scan mirror 22 on the secondunit 20 side has been driven to a scanning position which becomes thepath of the reflectors Tp1 and Tp2 and the light receiving element 14shown in FIG. 17A. If, at this timing, the scanning beam BM2 is normallyreflected by the reflectors Tp1 and Tp2 and received by the lightreceiving element 14, then as shown in FIG. 18, Sa′=1 is generated fromthe band pass filter 81, Sb′=1 is generated from the comparator 82, andSf=1 is generated from the logical product computing circuit 84. If thetiming signal TM=1 is periodically produced, and at this time Sb′=1 isgenerated, then Sf=1 is periodically generated from the logical productcomputing circuit 84. The pulse deficiency detecting circuit 85, whenSf=1 is generated at a predetermined period, generates V1=1. Here, theoff-delay time Tof2 of the off-delay circuit of the pulse deficiencydetecting circuit 85 is longer than the period for the output Sf=0generated from the logical product computing circuit 84 when normal timeand shorter than two periods for Sf=1 generation. Furthermore, theon-delay time of the on-delay circuit is set to be at least longer thanthe Sf=1 generation period.

[0117] On the other hand, if the scanning beam BM2 is not received atthe generating time of the timing signal TM=1 in which the scanning beamBM2 should be received as shown by the dotted line in FIG. 18, Sf=1 isnot generated from the logical product computing circuit 84 so that adeficiency occurs in the pulse, and the output from the pulse deficiencydetecting circuit 85 becomes V1=0. This signal V1 and the output Z1 fromthe signal deficiency detection circuit 15 are subjected to logicalproduct computation by the logical product computing circuit 86, and theresultant output ZV is made a signal indicating the presence/absence ofobject on the first unit 10 side.

[0118] With such a construction, if an object is present on an opticalpath so that the scanning beam BM2 is blocked, V1=0 results, and theoutput from the logical product computing circuit 86 becomes ZV=0indicating the presence of object. Furthermore, with a configurationprovided with such an optical path, if the positions of the two units 10and 20 are displaced from the normal position, the scanning beam BM2 isnot incident exactly onto the light receiving element 14, and hence isnot received. Therefore, this is also applicable to alignment of the twounits 10 and 20.

[0119] In FIG. 17, the case for one optical path is shown, however,reflectors may be added so that a plurality of optical paths areprovided. In this case, the timing signal TM=1 is generated for eachtiming at which the scanning beam BM2 should be received. Hence TM=1 isgenerated several times during one scanning period of the scan mirror22. Furthermore, instead of using the scanning beam BM2, a dedicatedlight emitting element for generating an optical beam having a frequencydifferent to those of the scanning beams BM1 and BM2 may be provided soas to form an optical path. Moreover, if the construction is such thatlight is continuously received, then the timing signal generatingcircuit 83 and the logical product computing circuit 84 becomeunnecessary.

[0120] The aforementioned ninth embodiment has been constructed using anoptical beam of a frequency different to that of the scanning beam BM1.However, it is also possible to make the wavelengths of the opticalbeams different. In this case, since the light receiving elements cannotbe shared, this may be processed with a construction where a separatelight receiving element and a separate amplifying circuit are providedand the two beams are separately received.

[0121] Next is a description of a suitable embodiment for use of theoptical barrier apparatus of the present invention as a safety ensuringfacility for a machine.

[0122] In order to use the optical barrier apparatus of the presentinvention as a safety ensuring facility for a machine, it is desirableto verify that the scanning beams BM1 and BM2 are reliably scanning thedetection area 1.

[0123]FIG. 19 through FIG. 21 show a configuration example of a scanningverification section serving as scanning verification means forperforming such verification. This scanning verification sectionverifies that a scanning mirror is scanning an optical beam within arange of a predetermined spread angle.

[0124]FIG. 19 shows a configuration example of the scanning verificationsection, FIG. 20 shows a block diagram of the scanning verificationsection, and FIG. 21 shows an operation time chart for the scanningverification section. The configuration of this scanning verificationsection is already known in PCT International Publication No.WO97/33186, and will be described briefly here.

[0125] In FIG. 19, reference numerals 101 and 102 denote a pair ofscanning verification light receiving elements, arranged outside of thedetection area, which receive optical beams 104 and 105 reflected tooutside of the detection area by a scan mirror 103. Reference numeral106 denotes a scanning verification signal processing circuit beingscanning verification signal deficiency detecting means, supplied withoutputs from the scanning verification light receiving elements 101 and102 to the input side thereof. The scanning verification signalprocessing circuit 106, as shown in FIG. 20, is constructed of a circuitthe same as the signal deficiency detection circuit 15 of FIG. 2,comprising light receiving circuits 106A and 106B, a comparator 106C,and a pulse deficiency detection circuit 106D, to detect an abnormalityof the scanning by an optical beam, from a pulse deficiency in thesignal from the light receiving elements 101 and 102.

[0126]FIG. 21 shows an operation time chart.

[0127] In the case where there is no reflection of the optical beam bythe scan mirror 103, or the scan mirror 103 does not rotate, or a faultsuch as reduction of rotation angle of the scan mirror 103 occurs, theoutput from at least one of the light receiving elements 101 and 102 islost, and as shown by the dotted line in the figure, a pulse deficiencyoccurs. Since an off-delay time Tof′ of then off-delay circuit insidethe pulse deficiency detection circuit 106D is set to be slightly longerthan the generation period of the light reception output, then when apulse deficiency occurs, the output from the pulse deficiency detectioncircuit 106D changes from H=1 to H=0, and while the fault as describedabove is continued so that the pulse deficiency periodically occurs, H=0is maintained, and the optical beam scanning abnormality is notified. Inorder to prevent automatic normal notification even when the abnormalityis no longer detected after the abnormality has once occurred, then forexample the signal H may be input to a flip-flop so that H=0 is stored.

[0128] In the case where such a scanning verification section is appliedto the optical barrier apparatus of the present invention, theaforementioned scanning verification sections are respectively providedin each unit 10 and 20, and as shown in FIG. 22, outputs H1 and H2 fromeach scanning verification section, and the signals Z1 and Z2 indicatingobject presence/absence of each unit 10 and 20 are respectivelysubjected to logical product computation by logical product computationcircuits 111 and 112, and each output for the computation results issubjected to logical product computation by logical product computationcircuit 113, and made the final output from the optical barrierapparatus. At this time, if the construction is such that the scanningverification light receiving elements 101 and 102 are respectivelyattached to opposite end portions of the reflector arrays 13 and 23 ofthe units 10 and 20, this has the advantage that it is possible toverify that the optical beams are being normally scanned at thepositions of the reflector arrays 13 and 23.

[0129] For the scan mirrors used in the abovementioned respectiveembodiments, for example commercial galvano-mirrors may be used.Furthermore, if semiconductor galvano-mirrors are used, the scan mirrorcan be made small, and consequently miniaturization of the opticalbarrier apparatus can be achieved.

[0130] As a semiconductor galvano-mirror, there is, in addition to alater mentioned electromagnetic type galvano-mirror, an electrostaticgalvano-mirror or a piezoelectric type galvano-mirror.

[0131] The electrostatic galvano-mirror is an element manufactured by asemiconductor element manufacturing process for moving a movable plateformed with a mirror by electrostatic force. This is disclosed forexample in Japanese Unexamined Patent Publication No. 5-60993.Furthermore, the piezoelectric type galvano-mirror is for moving amovable plate formed with a mirror by piezoelectric resonance, and isdisclosed for example in “Reprinted from Miniature and Micro-Optics;Fabrication and System Applications Volume 1554” of the SPIE-TheInternational Society for Optical Engineering, published July 1991.

[0132] Here is a detailed description of a suitable electromagnetic typegalvano-mirror serving as a scan mirror. The electromagnetic typegalvano-mirror to be described here is known for example from JapaneseUnexamined Patent Publication No. 8-220453 by the present applicant.

[0133]FIG. 23 is an exploded perspective view of an electromagnetic typesemiconductor galvano-mirror. In order to facilitate understanding, thisis shown in enlarged size.

[0134] In FIG. 23, on the inside of a silicon substrate mounted on aninsulating substrate, there is provided a torsion bar integrally formedwith the silicon substrate and a movable plate supported by the torsionbar. A planar coil is provided on the periphery of the movable plate,and a mirror is provided at the central portion of the movable plate.Permanent magnets are arranged on opposite side faces of the siliconsubstrate. The polarity of the permanent magnets is such that on oneside face of the silicon substrate, the top is N and the bottom is S,while on the other side face, the bottom is N and the top is S.

[0135] Regarding the operation, when a current flows in the planar coilfrom electrode terminals, the current flows so as to cross the staticmagnetic field of the permanent magnets, so that a force acts on theopposite ends of the movable plate according to Fleming's left-handrule, and the movable plates is rotated. When an AC current flows in theplanar coil, the movable plate is rotated periodically, so that theoptical beam incident on the mirror can be reflection scanned. Themovable plate resonates at a constant frequency, indicating a peak inthe amplitude. Consequently, since at the time of resonance a largedisplacement angle is obtained with a small input, it is desirable touse the galvano-mirror in the resonant condition.

[0136] With the respective embodiments of the optical barrier apparatusof the present invention described above, the detection area ismonitored with a construction where the optical beams from the lightemitting elements are reflected by the scan mirrors. However, thepresent invention is not limited to this, and for example theconstruction may be such that there is provided a scanning element of asemiconductor galvano-mirror type with a light emitting element mountedat the position of the scan mirror, and the light emitting element isrotated so that the detection area is scanned by an optical beam fromthe light emitting element.

[0137] In order to realize the optical barrier apparatus of theabovementioned respective embodiments with high safety, the signaldeficiency detection circuit and the scanning verification section maybe of a fail-safe construction. In the case where the threshold valuecomputation circuit and the logical product computation circuit used inthe respective circuits are configured so as to be fail-safe, then afail-safe window-comparator/AND gate such as disclosed in U.S. Pat. No.5,345,138, U.S. Pat. No. 4,661,880, and U.S. Pat. No. 5,027,114 can beused. These circuits and the operation and fail-safe characteristicshave been illustrated in the article such as TRAN. IEE of Japan, Vol.109-C, No. 9, September 1989 (A Method of Constructing an InterlockSystem using a Fail-Safe Logic Element having Window Characteristics, or“Application of Window Comparator to Majority Operation” Proc. of 19thInternational Symp. on Multiple-Valued Logic, IEEE Computer Society (May1989). As the on-delay circuit, it is possible to use a fail-safeon-delay circuit known for example from PCT International PublicationNumbers WO94/23303 and WO94/23496, Japanese Examined Patent PublicationNo. 1-23006 and Japanese Unexamined Patent Publication No. 9-162714. Thefail-safe construction of the rectifying circuit and the amplifyingcircuit is known for example from PCT/JP93/00411. Furthermore, theconstruction of a fail-safe band pass filter where the attenuationamount does not drop at the time of a fault, is shown in the articlesuch as Japanese Institute of Electrical Engineers IndustrialMeasurement Control Seminar documents, IIC-94-23, (94-7). By usingthese, the optical barrier apparatus may be constructed as a fail-safesafety apparatus which does not erroneously notify of the absence ofobject at the time of a fault.

Industrial Applicability

[0138] The present invention enables a reduction in cost of an opticalbeam scanning type optical barrier apparatus for scanning a detectionarea with an optical beam to monitor for objects, without narrowing thedetection area. Therefore industrial applicability is considerable.

What is claimed is:
 1. An optical barrier apparatus comprising a firstunit and a second unit facing each other with a detection areatherebetween, wherein each of said first and second units comprises:optical beam generating means; optical beam scanning means forreflecting an optical beam generated by said optical beam generatingmeans so as to scan an area containing said detection area; optical beamreflecting means for reflecting a scanning beam incident from saidoptical beam scanning means via said detection area by turning back atapproximately 180 degrees; light receiving means arranged in thevicinity of said optical beam scanning means for receiving a reflectionbeam from said optical beam reflecting means; and signal deficiencydetecting means for detecting the presence/absence of a deficiency ofoutput signal of said light receiving means and generating anotification output for object absence at the time of no deficiency, andwherein the optical beam scanning means and the light receiving means ofsaid first unit and the optical beam scanning means and the lightreceiving means of said second unit are arranged on either side of thedetection area at approximately diagonal positions.
 2. An opticalbarrier apparatus according to claim 1, wherein there is providedsynchronous drive means for synchronizing the two optical beam scanningmeans of said first and second units with respect to each other so thatwhen a scanning beam direction on said first unit side is a diagonaldirection, a scanning beam direction on said second unit side is also adiagonal direction.
 3. An optical barrier apparatus according to claim1, wherein there is provided selection drive means for selectivelydriving said first and second units so that object detection operationsof said first unit and second unit are not performed at the same time.4. An optical barrier apparatus according to claim 3, wherein there isprovided signal selection means constructed for outputting a firstselection signal and a second selection signal in complementary relationto each other from said selection drive means to the optical beamgenerating means of said first and second units to selectively drivesaid first and second units, for making an output from the signaldeficiency detecting means of said first unit valid when the opticalbeam generating means of said first unit is selectively driven with saidfirst selection signal, while making an output from the signaldeficiency detecting means of said second unit valid when the opticalbeam generating means of said second unit is selectively driven withsaid second selection signal.
 5. An optical barrier apparatus accordingto claim 1, wherein the emission wavelengths of optical beamsrespectively generated from the respective optical beam generating meansof said first unit and second unit are made different from each other.6. An optical barrier apparatus according to claim 1, wherein blinkingfrequencies of reflection beams respectively reflected from each opticalbeam reflecting means of said first unit and second unit are madedifferent from each other.
 7. An optical barrier apparatus according toclaim 6, wherein respective optical beam reflecting means of said firstand second units are made reflector arrays respectively comprising aplurality of reflectors, and a pitch between reflectors of said firstunit and a pitch between reflectors of said second unit are madedifferent from each other.
 8. An optical barrier apparatus according toclaim 6, wherein each optical beam reflecting means of said first andsecond units incorporates a plurality of reflecting portions divided byarranging a mask at spacing on one reflector, and a width of said maskof said first unit and a width of said mask of said second unit are madedifferent from each other.
 9. An optical barrier apparatus according toclaim 5, wherein each signal deficiency detecting means of said firstand second units incorporates signal extraction means for extractingonly an optical beam signal component of its own unit from an outputsignal of said light receiving means.
 10. An optical barrier apparatusaccording to claim 1, wherein each signal deficiency detecting meansverifies that a light reception output from said light receiving meansis one based on a reflection beam from said optical beam reflectingmeans, to generate a notification output for object absence.
 11. Anoptical barrier apparatus according to claim 10, wherein said signaldeficiency detecting means verifies that a reflection beam from at leastone previously determined specific reflector is periodically received,to generate a notification output for object absence.
 12. An opticalbarrier apparatus according to claim 11, wherein said specific reflectorincorporates modulation means for periodically driving said reflector toa position for reflecting a scanning beam in a direction of said lightreceiving means, and to a position where a scanning beam is notreflected in a direction of said light receiving means, to modulate areflection beam, and said signal deficiency detecting means verifiesthat an AC signal corresponding to a drive frequency of said specificreflector is being output from said light receiving means, to generate anotification output for object absence.
 13. An optical barrier apparatusaccording to claim 10, wherein when said optical beam reflecting meansis constructed to be divided into a plurality of reflecting portions,said signal deficiency detecting means counts the pulse number of lightreception outputs of said light receiving means per one scanning period,to generate a notification output for object absence when a countedvalue coincides with the number of reflecting portions of said opticalbeam reflecting means.
 14. An optical barrier apparatus according toclaim 1, wherein said signal deficiency detecting means verifies that anoptical beam other than a scanning beam from its own unit isperiodically received via said detection region, to generate anotification output for object absence.
 15. An optical barrier apparatusaccording to claim 14, wherein a reflector for reflecting a scanningbeam from another unit so as to be received by the light receiving meansvia said detection area is separately provided, and said signaldeficiency detecting means verifies that there is a light receptionoutput based on the scanning beam from said other unit at a scanningtiming in which the scanning beam from said other unit is incident ontosaid reflector, to generate a notification output for object absence.16. An optical barrier apparatus according to claim 1, wherein scanningverification means for verifying that the scanning beam is scannedwithin a range of area including the detection area is provided in eachunit.
 17. An optical barrier apparatus according to claim 16, whereinsaid scanning verification means comprises a pair of scanningverification light receiving elements arranged outside said detectionarea, and scanning verification signal deficiency detecting means fordetecting the presence/absence of a deficiency of output signal of saidpair of scanning verification light receiving elements, to generate anoutput indicating scanning normalcy when there is no deficiency.
 18. Anoptical barrier apparatus according to claim 1, wherein a retroreflectoris used in said optical beam reflecting means.